Federal Standardization Procedures require that the "WALK" symbol be illuminated in lunar white and that the "DONT WALK" symbol be illuminated in Portland orange. This has necessitated the use of mercury vapor tubular lamps to illuminate the "WALK" symbol. However, problems have been encountered because of the tendency of the mercury vapor lamp to fail to be illuminated when energized, especially in cold weather.
The problem is resolved in accordance with the present invention by providing a heat conductive path from the neon lamp in the "DONT WALK" compartment (which normally encounters no start-up problems) to the mercury vapor lamp in the "WALK" compartment. This causes the mercury vapor lamp to be kept in a warm state when it is de-energized, and assures that the mercury vapor lamp will become illuminated the instant it is again energized.